1. Field of the Invention
The present invention relates to an atmospheric pressure estimation device that estimates an atmospheric pressure, which is an engine control parameter, in an outboard motor for small boat unequipped with a battery and configured to start an engine by manually rotating a crankshaft.
2. Description of the Background Art
A fuel supply by a calibrator method is the mainstream for an outboard motor for small boat of a small piston displacement. Normally, the outboard motor is not equipped with a battery or a starter but provided with a recoil starting device to start the engine manually by a ship driver, so that the outboard motor is formed to be lightweight and at low costs.
The fuel supply method of an outboard motor for small boat of a small piston displacement is now also changing from carburetor to electronic control with the aim of enhancing the ease of operation and maintenance as well as an output performance and addressing an emission gas issue. Nevertheless, in order to form a compact, light, inexpensive engine, a starting device, such as a starter, and a battery are often omitted.
Also, an amount of intake air to the engine varies with an atmospheric pressure and it is therefore necessary to control the engine according to an atmospheric pressure. It is, however, preferable for an outboard motor for small boat of a small piston displacement to reduce the number of sensors used to calculate control parameters to the least extent possible. To this end, an atmospheric pressure sensor is often omitted, and an atmospheric pressure is estimated instead on the basis of information from other sensors, such as intake pressure sensor and a throttle sensor, and an operation state, so that the estimated atmospheric pressure is used as a control parameter.
In the related art, Patent Document 1 proposes a method of estimating an atmospheric pressure, by which means for detecting an amount of air taken into the engine is used, so that a calculation value and an actual measured value of an amount of intake air to the engine are controlled to be equal using an intake pressure sensor, a throttle sensor, an operation state of the engine, and the estimated atmospheric pressure value.
[Patent Document 1] WO 2010-090060
As described above, in the atmospheric pressure estimation device in an outboard motor for small boat unequipped with a battery and configured to manually rotate the crankshaft so that an electronic control unit is activated with power generated by the rotation to start and control the engine, the electronic control unit is activated while the engine is in operation. Also, the power supply of the electronic control unit is immediately turned OFF when the engine stops because generated power is no longer supplied.
Hence, immediately after the electronic control unit is activated, the engine is already driven and so-called an engine stall state does not occur. An intake pressure value at the engine start is unstable and is not equal to an atmospheric pressure. It is therefore difficult to estimate an atmospheric pressure in a stable manner from the intake pressure value found by the intake pressure sensor immediately after the electronic control unit is activated.